The present invention tackles the problem of controlling gear shifting in cycles and has been developed with particular attention paid to the possible application to competition bicycles. In any case, the reference to this possible application, and in particular the reference to the application to racing bicycles, must not be interpreted as limiting the possible field of application of the invention.
Over the last few years there has developed, in the cycle sector, the tendency to associate to the cycle sensors of various nature so as to be able to acquire information of various kinds regarding the use/behaviour of the means, the aim being to be able to intervene through actuators to modify—according to certain criteria, and acting both in an automatic way and according to specific commands issued by the user ? the conditions of use/behaviour of the means, in particular as regards its set.
In particular, the present invention has been developed with specific reference to the servo systems which carry out positioning of the transmission chain of the cycle in a position corresponding to the front derailleur and to the rear derailleur.
In drive trains mounted on cycles of a more sophisticated type it is envisaged that the toothing of the crankwheel and sprockets on which the derailleurs act are not all made up of teeth that are the same. Instead, the teeth are arranged in ordered sets and the teeth comprised within each set have a sequence of differentiated geometries such as to facilitate shifting of the chain, the foregoing in order to create, within the corresponding toothing, points or areas in which the movement of shifting of the chain is facilitated. Said points or areas are referred to simply as “facilitating portions”.
If a command for shifting of the chain position is issued at an inopportune moment, the correct positioning of the chain may be at least momentarily hindered, and hence delayed.
This drawback, which is anyway noticeable in systems for control of gear-shifting of a manual type, becomes particularly troublesome in cycles in which the change of transmission ratio is controlled by an automatically operated actuator, which is governed by an electronic control system. Such a system is usually configured to co-ordinate the various interventions of modification of set of the cycle itself (both according to the commands issued by the user and in an altogether automatic way), so as to optimize the performance of the cycle and, more in general, of the cycle-user system.
As is recognized, for example, in the European patent application EP-A-1 010 612 (on the other hand published after the date of priority of the present application), in the framework of these systems, the attempt to control shifting of the chain at a wrong moment may give rise to various problems.
For example, in addition to an undesired retardation in actuation of the command, a problem may arise linked to the fact that the actuator involved by the command ends up being activated (and hence absorbing energy) for an interval of time in which the actuator itself is not able to ensure that the action requested will be carried out. During this interval, the actuator absorbs power from supply sources (typically batteries) mounted on the cycle, this amounting to energy which, to all effects, ends up being wasted without obtaining any useful result.